Additional Banner sized aspect ratio?

I would love to be able to generate a banner-sized image as I often create graphics to place at the top of documents, websites, web headers, Slack canvas headers, and normally the widescreen content is too tall to really create anything useable. I know I could create content from Photoshop but I love the ease and speed of generating right in Adobe Firefly. Starting with a thinner but wide aspect ratio would help me create useable content very quickly for these other uses.